We present the results of measurements of the analysing power for the p(pol)p
--> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret
these results within the framework of the meson exchange models. The determined
values of the analysing power at both excess energies are consistent with zero
implying that the eta meson is produced predominantly in s-wave.Comment: 3 pages, 3 figures, Presented at the Workshop on the physics of
  excited nucleons (NSTAR 2007), 5-8 September 2007, Bonn, German

Adam, H. -H.

Budzanowski, A.

Czerwinski, E.

Czyzykiewicz, R.

Gil, D.

Grzonka, D.

Hodana, M.

Janusz, M.

Jarczyk, L.

Kamys, B.

Khoukaz, A.

Kilian, K.

Klaja, P.

Lorentz, B.

Moskal, P.

Oelert, W.

Piskor-Ignatowicz, C.

Przerwa, J.

Rejdych, B.

Ritman, J.

Sefzick, T.

Siemaszko, M.

Silarski, M.

Smyrski, J.

Taschner, A.

Ulbrich, K.

Winter, P.

Wolke, M.

Wustner, P.

Zielinski, M. J.

Zipper, W.

English

arXiv

Piskor-Ignatowicz, B.

Adam, H.-H.

Täschner, A.

Wüstner, P.

Zielinski, M.

Juelich Shared Electronic Resources

Dynamics of the near threshold eta meson production in proton-proton interaction

arXiv:0711.4998v2  [nucl-ex]  29 Jul 2008EPJ manuscript No.(will be inserted by the editor)Dynamics of the near threshold η meson production inproton-proton interactionR. Czyz˙ykiewicz1,2, P. Moskal1,2, H.-H. Adam3, A. Budzanowski4, E. Czerwin´ski1, D. Gil1, D. Grzonka2,M. Hodana1,2, M. Janusz1,2, L. Jarczyk1, B. Kamys1, A. Khoukaz3, K. Kilian2, P. Klaja1,2, B. Lorentz2, W. Oelert2,C. Piskor-Ignatowicz1, J. Przerwa1,2, B. Rejdych1, J. Ritman2, T. Sefzick2, M. Siemaszko5, M. Silarski1, J. Smyrski1,A. Ta¨schner3, K. Ulbrich6, P. Winter7, M. Wolke2, P. Wu¨stner2, M. J. Zielin´ski1, W. Zipper51 Institute of Physics, Jagellonian University, 30-059 Cracow, Poland2 IKP & ZEL, Forschungszentrum Ju¨lich, 52425 Ju¨lich, Germany3 IKP, Westfa¨lische Wilhelms-Universita¨t, 48149 Mu¨nster, Germany4 Institute of Nuclear Physics, 31-342 Cracow, Poland5 Institute of Physics, University of Silesia, Katowice, Poland6 ISK, Rheinische Friedrich-Wilhelms-Universita¨t, 53115 Bonn, Germany7 Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USAReceived: date / Revised version: dateAbstract. We present the results of measurements of the analysing power for the pp → ppη reaction atthe excess energies of Q = 10 and 36 MeV, and interpret these results within the framework of the mesonexchange models. The determined values of the analysing power at both excess energies are consistent withzero implying that the η meson is produced predominantly in s-wave.PACS. 14.40.-n Mesons – 14.40.Aq pi, K, and η mesons – 13.60.Le Meson production1 IntroductionFrom the precise measurements of the total cross sectionfor the η meson production in the pp → ppη reactionin the close-to-threshold region [1,2,3,4,5,6,7,8] it wasconcluded [9,10,11,12,13,14,15,16,17] that this processproceeds through the excitation of one of the protons tothe S11(1535) state, which subsequently deexcites via theemission of the η meson and a proton. However, there areplenty of possible scenarios of the excitation of S11(1535)resonance. In fact, exchange of any of the pi, η, ω, or ρmesons may contribute to the resonance creation. Consid-ering the cross sections itself doesn’t answer the questionwhich out of these mesons give the significant contributionto the production amplitude.Some constraints may be deduced from the investiga-tions of the isospin dependence of the total cross sectionfor the NN → NNη reaction [18]. The ratio of the to-tal cross sections for the η meson production in proton-neutron collisions to the analogous cross section with proton-proton colliding in the initial state was found to be about6.5 in the close-to-threshold region, which revealed strongisospin dependence of the production process. This meansthat the production of the η meson with the total isospinI=0 in the initial channel exceeds the production withthe isospin I=1 by a factor of 12, suggesting [19] that theisovector meson exchange - the pi or ρ meson exchange -is the dominant process leading to the excitation of theS11 resonance. However, the relative contributions of thepseudoscalar pi meson and vector ρ meson still remain tobe determined.Here, the measurements of the polarization observablescan assist, because the predictions of the one boson ex-change models [16,17] with respect to the analysing powerare sensitive to the type of the exchanged meson.COSY-11 collaboration performed two measurementsof the analysing power function at the beam momenta ofpbeam = 2.010 GeV/c and 2.085 GeV/c, which for thepp → ppη reaction correspond to the excess energies ofQ=10 and 36 MeV, respectively. Here we would like tobriefly summarize the results of these measurements andpresent the main conclusions we could have drawn fromour studies.2 ResultsIn the measurements the COSY-11 detection setup [20,21,22] has been used, along with the vertically polarizedproton beam, which polarization was flipped from cycleto cycle in order to reduce the systematic uncertainties.For the detailed description of the experimental apara-tus, method of measurement and analysis, the reader isreferred to [23].The tested predictions of the analysing power of ref-erence [16] were based on the assumption of the ρ meson2 R. Czyz˙ykiewicz, P. Moskal et al.: Dynamics of the near threshold η meson production in proton-proton interactionexchange dominance and the proton asymmetries takenfrom the photoproduction of the η meson [26]. In the caseof the calculations of reference [17] the exchanges of allmesons have been taken into account in the framework ofthe relativistic meson exchange model of hadronic interac-tions and it was found in this model that the contributionfrom the pion exchange is the dominant one.Fig. 1 shows the experimentally determined values ofthe analysing power Ay for the pp → ppη reaction con-fronted with the theoretical predictions of the pseudoscalar [17]and vector [16] meson exchange dominance models. Theχ2 test of the correctness of these models have been per-formed and the reduced values of the χ2 were found tobe equal to 0.54 (corresponding to the significance level ofαpsc = 0.81) and 2.76 (αvec = 0.006), for pseudoscalar andvector meson exchange dominance models, respectively.-1-0.500.51-1 -0.5 0 0.5 1cos(Θη)Q=10 MeVAy-1-0.500.51-1 -0.5 0 0.5 1cos(Θη)Q=36 MeVAyFig. 1. Analysing power Ay for the pp → ppη reaction as afunction of cosine of the polar angle of the η meson produc-tion in the overall center-of-mass system for Q=10 MeV (leftpanel) and Q=36 MeV (right panel). Full lines are the pre-dictions based on the pseudoscalar meson exchange model [17]whereas the dotted lines represent the calculations based on thevector meson exchange [16]. In the right panel the dotted lineis consistent with zero. Shown are the statistical uncertainties.In the vector meson exchange dominance model [16]the angular distribution of the analysing power is param-eterized as a function of the polar angle of η meson pro-duction in the center-of-mass system with the followingequation:Ay(θη) = Amax,vecy sin 2θη, (1)where the amplitude Amax,vecy is a function of the excessenergy Q, shown as a dotted line in the left panel of Fig. 2.We have estimated the values of Amax,vecy comparingthe experimental data with predicted shape utilizing aχ2 test [23,24,25]. Determined experimental values areshown in Fig. 2 (left) along with the theoretical predic-tions according to the vector meson exchange dominancemodel [16]. Analogously, the confrontation of the exper-imentally determined amplitude Amax,pscy with the pre-dictions of the pseudoscalar meson exchange dominancemodel [17] are shown in Fig. 2 (right). Predictions of themodel based on the pi mesons dominance are fairly consis-tent with the data, whereas the calculations based on thedominance of the ρmeson exchange differ from the data by-0.2-0.100.10.20 10 20 30 40Q [ MeV ]Aymax,vec-0.2-0.100.10.20 10 20 30 40Q [ MeV ]Aymax,pscFig. 2. Theoretical predictions for the energy dependence ofthe amplitude of Amaxy confronted with the amplitudes deter-mined experimentally at the excess energies of Q=10 and 37MeV for the vector (left) and pseudoscalar (right) meson ex-change dominance model.more than four standard deviations. However, the lattercalculation used the proton asymmetry (T ) in eta photo-production [26], within the framework of the vector mesondominance model [27], as the basis of their estimate. Itshould be noted that it has proved hard to reconcile theexperimental value of T with the results of photoproduc-tion amplitude analyses [28].3 Conclusions and outlookTaking into account the χ2 analysis of the analysing powerfor the pseudoscalar and vector meson exchange modelswe have shown that the predictions of the pseudoscalarmeson exchange dominance [17] are in line with the ex-perimental data at the significance level of 0.81. On theother hand, the assumption that the η meson is producedsolely via the exchange of the ρ meson [16], leads to thediscrepancy between the theoretical predictions and ex-perimental data larger than four standard deviations. Itmust be stated, however, that the production amplitudefor the ρ meson exchange was determined based on thevector meson dominance hypothesis and the photoproduc-tion data [26]. At this point it is also worth mentioningthat the recent calculations of the η meson production inthe NN collisions performed in the framework of the effec-tive Lagrangian model [29] also indicate the dominance ofthe pion exchange.The analysing power values for both excess energies areconsistent with zero within one standard deviation. Thisis in line with the results obtained by the DISTO [30] col-laboration in the far-from-threshold energy region. Sucha result may indicate that the η meson is predominantlyproduced in the s-wave.4 Future perspectivesRecently, the proposal for the measurement of the analyz-ing power function [31] with the WASA-at-COSY apara-tus [32] has been presented and awaits recommendationR. Czyz˙ykiewicz, P. Moskal et al.: Dynamics of the near threshold η meson production in proton-proton interaction 3of the COSY Programme Advisory Committee. Measure-ments are planned with about 50 times better statisticswhich should enable the error bars from Fig. 1 to be re-duced of circa 7 times.-1-0.500.51-1 -0.5 0 0.5 1cos(Θη)Q=10 MeVAy-1-0.500.51-1 -0.5 0 0.5 1cos(Θη)Q=40 MeVAyFig. 3. Predictions of the dependence of the analyzing powerfunction on the intermediate resonance type [33].Fig. 3 presents the dependence of the analyzing poweras a function of the cosine of the polar angle of the ηmeson emission in the center-of-mass system on the inter-mediate resonance type [33]. Solid line are the calculationsof the pseudoscalar meson exchange model performed un-der assumption that only S11(1535) resonance contributesto the η meson production amplitude, whereas the dot-ted line represent the predictions of the same model, in-cluding D13(1520), S11(1535), S11(1650), and D13(1700)resonances. Therefore, the improvement in the measure-ment accuracy would enable to investigate the influenceof other-than-S11(1535) resonances upon the productionamplitude.Measurements of the analysing power Ay with muchhigher statistics may also allow the model independentpartial wave decomposition with an accuracy by far betterthan resulting from the measurements of the distributionsof the spin averaged cross sections. This is because thepolarization observables can probe the interference termsbetween various partial amplitudes, even if they are neg-ligible for the spin averaged distributions. More impor-tantly, in case of the pp → ppX reaction the interferenceterms between the transition with odd and even valuesof the angular momentum of the final state baryons arebound to vanish for the cross sections [34,35]. This char-acteristic is due to the invariance of all observables underthe exchange of identical nucleons in the final state. Due tothe same reason there is no interference between s and p-waves of the η meson in the differential cross sections [35].However, s-p interference does not vanish for the protonanalysing power, and thus the precise measurements ofAy could provide the first determination of the compar-atively small p-wave contribution [35], unreachable fromspin averaged observables.5 AcknowledgmentWe acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 programme(Hadron Physics, N4:EtaMesonNet, RII3-CT-2004-506078),the support of the Polish Ministry of Science and HigherEducation under the grants No. PB1060/P03/2004/26,3240/H03/2006/31 and 1202/DFG/2007/03, and the sup-port of the German Research Foundation (DFG) under thegrant No. GZ: 436 POL 113/117/0-1.References1. F. Hibou et al., Phys. Lett. B 438 (1998) 41;2. J. Smyrski et al., Phys. Lett. B 474 (2000) 182;3. A. M. Bergdolt et al., Phys. Rev. D 48 (1993) 2969;4. E. Chiavassa et al., Phys. Lett. B 322 (1994) 270;5. H. Cale´n et al., Phys. Lett. B 366 (1996) 39;6. H. Cale´n et al., Phys. Rev. Lett. 79 (1997) 2642;7. P. Moskal et al., Phys. Rev. C 69 (2004) 025203;8. M. Abdel-Bary et al., Eur. Phys. J. A 16 (2003) 127.9. A. Moalem et al., Nucl. Phys. A 600 (1996) 445.10. M. Batinic´ et al., Phys. Scripta 56 (1997) 321.11. J. F. Germond et al., Nucl. Phys. A 518 (1990) 308.12. J. M. Laget et al., Phys. Lett. B 257 (1991) 254.13. T. Vetter et al., Phys. Lett. B 263 (1991) 153.14. B. L. Alvaredo et al., Phys. Lett. B 324 (1994) 125.15. V. Bernard et al., Eur. Phys. J. A 4 (1999) 259.16. G. Fa¨ldt and C. Wilkin, Phys. Scripta 64 (2001) 427.17. K. Nakayama et al., Phys. Rev. C 65 (2002) 045210.18. H. Cale´n et al., Phys. Rev. C 58 (1998) 2667.19. C. Wilkin, Report No. TSL/ISV-96-0147 (1996).20. S. Brauksiepe et al., Nucl. Instr. and Meth. A 376 (1996)397.21. J. Smyrski et al., Nucl. Instr. and Meth. A 541 (2005)574.22. P. Klaja et al., AIP Conf. Proc. 796 (2005) 160.23. R. Czyz˙ykiewicz, nucl-ex/0702010, PhD. Dissertation,Jagellonian University (2007).24. R. Czyz˙ykiewicz et al., Phys. Rev. Lett. 98 (2007) 122003.25. R. Czyz˙ykiewicz et al., Int. J. Mod. Phys. A22 (2007) 518.26. A. Bock et al., Phys. Rev. Lett. 81 (1998) 534.27. J. J. Sakurai, Annals Phys. 11 (1960) 1.28. W.-T. Chiang, S.-N. Yang, L. Tiator, and D. Drechsel,Nucl. Phys. A 700 (2002) 429.29. R. Shyam, Phys. Rev. C 75 (2007) 055201.30. F. Balestra et al., Phys. Rev. C 69 (2004) 064003.31. P. Moskal, M. Hodana et al., COSY Proposal No. 185(2007).32. H.-H. Adam et al., Proposal for WASA-at-COSY,nucl-ex/0411038.33. K. Nakayama, private communication (2007).34. A. Deloff, Phys. Rev. C 69 (2004) 035206.35. C. Wilkin, private communications (2007).

R. Czyżykiewicz

P. Moskal

H.-H. Adam

A. Budzanowski

E. Czerwiński

D. Gil

D. Grzonka

M. Hodana

M. Janusz

L. Jarczyk

B. Kamys

A. Khoukaz

K. Kilian

P. Klaja

B. Lorentz

W. Oelert

C. Piskor-Ignatowicz

J. Przerwa

B. Rejdych

J. Ritman

T. Sefzick

M. Siemaszko

M. Silarski

J. Smyrski

A. Täschner

K. Ulbrich

P. Winter

M. Wolke

P. Wüstner

M. Zieliński

W. Zipper

Crossref

Dynamics of the near threshold η meson production in proton-proton interaction

Czyżykiewicz, Rafał

Moskal, Paweł

Czerwiński, Eryk

Gil, Damian

Hodana, Małgorzata

Janusz, Michał

Jarczyk, Lucjan

Kamys, Bogusław

Klaja, Paweł

Piskor-Ignatowicz, Cezary

Przerwa, Joanna

Rejdych-Iwanek, Barbara

Silarski, Michał

Smyrski, Jerzy

Zieliński, Marcin

Jagiellonian Univeristy Repository

Dynamics of the near threshold $\eta$ meson production in proton-proton interaction

Dynamics of the near threshold eta meson production in proton-proton
  interaction

Dynamics of the near threshold eta meson production in proton-proton interaction

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Juelich Shared Electronic Resources

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Jagiellonian Univeristy Repository